Scientists and engineers have been working on the problem of electronic, automatic noise cancelling (ANC) for decades. The basic physics of wave propagation suggests it is possible to create an “anti-noise” wave that is 180 degrees out of phase with the noise signal, and cancel the noise completely through destructive interference. This works reasonably well for simple, repetitive, low-frequency sounds. However, it does not work well for dynamic, rapidly changing sounds, or those containing higher frequencies.
The best current systems (using a hybrid design combining feed forward and feedback), can reduce repetitive noise (like an engine or fan) at frequencies up to 2 kHz using variants of LMS (Least Mean Square) Adaptive Filtering to create the anti-noise signal by repetitively estimating the transfer function that will create the least noise practical at the output. Although companies continue to invest in improving ANC results, their activity appears to be focused on improving upon these existing techniques Moreover, despite having greater processing power available, it appears that ANC using various adaptive filters has an upper frequency limit somewhere below 4 kHz and the ability to attenuate signals by between 10 dB and 30 dB.